import java.util.*;

class TreeNode {
      int val;
      TreeNode left;
      TreeNode right;
      TreeNode() {}
      TreeNode(int val) { this.val = val; }
      TreeNode(int val, TreeNode left, TreeNode right) {
          this.val = val;
          this.left = left;
          this.right = right;
     }
  }

class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> listall=new ArrayList<>();

        Queue<TreeNode> queue=new LinkedList();

        queue.add(root);
        while(!queue.isEmpty()){
            List<Integer> list=new ArrayList();
            for (int i = queue.size(); i> 0 ; i--) {
                TreeNode node= queue.poll();
                list.add(node.val);

                if(node.left!=null) {
                    queue.add(node.left);

                }
                if(node.right!=null) {
                    queue.add(node.right);

                }

            }

            listall.add(list);



        }
        return listall;



    }
}